The present invention relates to semiconductor devices, and in particular, relates to a semiconductor device comprising a memory transistor which stores data by a change in the level of a threshold voltage.
Conventionally, a nonvolatile semiconductor memory device (semiconductor device) comprises a plurality of memory transistors and a drive circuit provided corresponding to each memory transistor. Each drive circuit includes a P-type transistor whose source receives a positive voltage higher than a power supply voltage and whose drain is coupled to a gate of the corresponding memory transistor, and an N-type transistor whose drain is coupled to the gate of the corresponding memory transistor and whose source receives a reference voltage. The gate of the P-type transistor and the gate of the N-type transistor are coupled to each other.
In a write operation, a reference voltage is applied to the gates of two transistors of the drive circuit corresponding to a selected memory transistor of the memory transistors. Thus, the P-type transistor is turned on and the N-type transistor is turned off, and a positive voltage is applied to the gate of the selected memory transistor and data is written (e.g., see Japanese Patent Laid-Open No. 2001-243786 (Patent Document 1)).
Moreover, there is a nonvolatile semiconductor device that separates the gate of the P-type transistor from the gate of the N-type transistor of the drive circuit to separately control these two transistors. In this device, in switching the output voltage of the drive circuit, one transistor in a conductive state of the two transistors is caused to transition to a non-conductive state and subsequently the other transistor in a non-conductive state is caused to transition to a conductive state. Thus, the breakdown of the transistors can be prevented (e.g., see Japanese Patent Laid-Open No. 2003-77283 (Patent Document 2)).